Light detection and ranging receiver with avalanche photodiodes

ABSTRACT

A light detection and ranging (lidar) receiver may include a first photodiode, a first amplifier connected to the first photodiode, and a first analog-to-digital converter (ADC) connected to an output of the first amplifier. The lidar receiver may include a second photodiode, a second amplifier connected to the second photodiode, and a second ADC connected to the second amplifier. The lidar may include a processor connected to an output of the first ADC and an output of the second ADC and a direct-current-to-direct-current converter connected to an output of the processor and to the first photodiode and the second photodiode. The processor may determine, based on the output of the first ADC and the output of the second ADC, a first bias to apply to the first photodiode and a second bias to apply to the second photodiode.

RELATED APPLICATION

This application claims priority under 35 U.S.C. § 119 to U.S.Provisional Patent Application No. 62/895,813, filed on Sep. 4, 2019 andentitled “ACTIVE BALANCING FOR IMPROVED COMMON MODE REJECTION INCOHERENT RECEIVERS USING AVALANCHE PHOTODETECTOR AND LIDAR WITH SLOW ANDFAST ANALOG-TO-DIGITAL CONVERTERS,” the content of which is incorporatedby reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates to light detection and ranging (lidar)systems and, more particularly, to a lidar receiver with avalanchephotodiodes.

BACKGROUND

A measurement system may be used for depth-sensing measurements. Forexample, a lidar system may transmit pulses of laser light, and maymeasure reflected pulses to determine a distance of an object from thelidar system. In this case, the lidar system may perform atime-of-flight measurement of the laser pulse and may generate athree-dimensional representation of an object. A frequency-modulatedcontinuous-wave (FMCW) lidar system may transmit continuous laser lightaccording to a prescribed, continuous variation in frequency. In thiscase, the FMCW lidar system may determine a frequency difference betweena received signal and a transmitted signal to generate athree-dimensional representation of an object.

SUMMARY

According to some implementations, a lidar system may include atransmitter to transmit an optical beam, and a receiver to receive areflection of the optical beam, the receiver comprising: a firstphotodiode to generate a first analog signal that is based at least inpart on the reflection of the optical beam; a first amplifier to obtainthe first analog signal from the first photodiode; a firstanalog-to-digital converter (ADC) to derive a first digital signal basedon the first analog signal; a second photodiode to generate a secondanalog signal that is based at least in part on the reflection of theoptical beam; a second amplifier to obtain the second analog signal fromthe second photodiode; a second ADC to derive a second digital signalbased on the second analog signal; a processor to determine, based onthe first digital signal and the second digital signal, a first bias toapply to the first photodiode and a second bias to apply to the secondphotodiode, wherein, when the first bias is applied to the firstphotodiode and the second bias is applied to the second photodiode, afirst current associated with the first analog signal corresponds to asecond current associated with the second analog signal; and adirect-current-to-direct-current converter to apply the first bias tothe first photodiode and to apply the second bias to the secondphotodiode.

According to some implementations, a lidar receiver may include a firstphotodiode; a first amplifier connected to the first photodiode; a firstADC connected to an output of the first amplifier; a second photodiode;a second amplifier connected to the second photodiode; a second ADCconnected to an output of the second amplifier; a processor connected toan output of the first ADC and an output of the second ADC; and adirect-current-to-direct-current converter connected to an output of theprocessor and to the first photodiode and the second photodiode.

According to some implementations, a method may include generating, by alidar receiver, using a first photodiode, and based at least in part ona reflection of an optical beam, a first analog signal; deriving, by thelidar receiver and based on the first analog signal, a first digitalsignal; generating, by the lidar receiver, using a second photodiode,and based at least in part on the reflection of the optical beam, asecond analog signal; deriving, by the lidar receiver and based on thesecond analog signal, a second digital signal; and determining, by thelidar receiver and based on the first digital signal and the seconddigital signal, a first bias to apply to the first photodiode and asecond bias to apply to the second photodiode, wherein, when the firstbias is applied to the first photodiode and the second bias is appliedto the second photodiode, a first current associated with the firstanalog signal corresponds to a second current associated with the secondanalog signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an example implementation described herein.

FIG. 2 is a diagram of an example lidar system described herein.

FIG. 3 is a diagram of an example lidar receiver described herein.

FIG. 4 is a flowchart of an example process for lidar detection.

DETAILED DESCRIPTION

The following detailed description of example implementations refers tothe accompanying drawings. The same reference numbers in differentdrawings may identify the same or similar elements.

A lidar system may use coherent detection to measure reflected pulses todetermine a distance of an object from the lidar system. For example,the lidar system may include a lidar receiver including a pair ofphotodiodes to generate, based on reflected pulses, photocurrents whichmay be used to determine the distance of the object from the lidarsystem. A signal-to-noise ratio (SNR) in the photocurrents may impactperformance of the lidar system, where higher SNRs may correspond tobetter performance than lower SNRs. The lidar system may include a laser(e.g., a laser diode) having a relative intensity noise (RIN), which mayincrease over time, due to temperature changes, and/or the like, and mayreduce the SNR. Using coherent detection, the lidar receiver may use acommon mode rejection ratio (CMRR) to cancel the RIN and increase theSNR.

FIG. 1 is a diagram of an example implementation 100 described herein.As shown in FIG. 1, the CMRR may be related to a photocurrent ratio(Alpha), where Alpha is a ratio of the photocurrents from thephotodiodes in the pair of photodiodes of the lidar receiver. A CMRRhaving a more negative number may be referred to as a higher CMRR thananother CMRR having a less negative number. In some implementations, ahigher CMRR (e.g., a more negative number) may increase the SNR of thelidar receiver and improve performance of the lidar system (e.g.,increase and/or maintain a maximum distance measurement and/or thelike). As shown in FIG. 1, a lidar receiver with an Alpha near one mayhave a high CMRR. Thus, a lidar receiver may include photodiodes havingbalanced photocurrents to achieve an Alpha near one.

A lidar receiver may include a pair of p-i-n (PIN) photodiodes togenerate, based on reflected pulses, photocurrents and a pair offeedback-controlled optical attenuators to attenuate the reflectedpulses received by the PIN photodiodes to balance the photocurrents ofthe PIN photodiodes. However, lidar receivers including such opticalattenuators may be expensive to manufacture and may suffer from highinsertion loss.

Another lidar receiver may include a pair of PIN photodiodes togenerate, based on reflected pulses, photocurrents and a transimpedanceamplifier (TIA) for each of the PIN photodiodes. However, the two TIAswould generate twice as much thermal noise and even greater shot noise,thereby reducing the SNR. Additionally, or alternatively,characteristics of the TIAs may not change in a same manner as atemperature of the lidar system changes.

According to some implementations described herein, a lidar receiver mayinclude a first photodiode (e.g., a first avalanche photodiode and/orthe like) and a second photodiode (e.g., a second avalanche photodiodeand/or the like), where the first photodiode and the second photodiodegenerate, based on a reflected optical beam, a first signal and a secondsignal, respectively. In some implementations, the lidar receiver mayinclude a processor to determine, based on the first signal and thesecond signal, a first bias to apply to the first photodiode and asecond bias to apply to the second photodiode, where, when the firstbias is applied to the first photodiode and the second bias is appliedto the second photodiode, a first current associated with the firstanalog signal corresponds to a second current associated with the secondanalog signal. In some implementations, the lidar receiver may include adirect-current-to-direct-current converter to apply the first bias tothe first photodiode and to apply the second bias to the secondphotodiode. In this way, the lidar receiver may balance the firstphotocurrent and the second photocurrent to achieve an Alpha near one, ahigher CMRR, an improved SNR, improved performance of a lidar systemincluding the lidar receiver, and/or the like.

In some implementations, the first photodiode and/or the secondphotodiode may be avalanche photodiodes, which may be less expensivethan using optical attenuators to balance photocurrents and may havelower insertion losses than when using optical attenuators. In someimplementations, the lidar receiver may balance the first photocurrentand the second photocurrent without generating additional thermal noise,shot noise, and/or the like, which may be generated by TIAs.

In some implementations, a lidar system may include the lidar receiverand a laser. As the RIN of the laser changes over time, due totemperature changes, and/or the like, the lidar receiver may maintainbalance of the first photocurrent and the second photocurrent, and maymaintain performance of the lidar system.

FIG. 2 is a diagram of an example lidar system 200 described herein. Asshown in FIG. 2, the lidar system 200 may include a laser, an opticalsystem, a scanner, a local oscillator, and a receiver. In someimplementations, the laser may generate a source beam (e.g., a laserbeam, an optical beam, and/or the like) and provide the source beam tothe optical system, and the optical system may provide the source beamto the scanner. As shown in FIG. 2, the scanner may tilt angularly toscan the source beam across a field of view, and may receive a beamreflected from the field of view (e.g., reflected from an object in thefield of view and/or the like). In some implementations, the scanner mayprovide the reflected beam to the optical system.

As shown in FIG. 2, the laser may also provide the source beam to thelocal oscillator, and the local oscillator may provide the source beamto the receiver. As also shown in FIG. 2, the optical system may providethe reflected beam to the receiver. The receiver may convert the sourcebeam from the local oscillator and the reflected beam into an outputsignal (e.g., a digital output signal and/or the like). In someimplementations, the lidar system 200 may include one or moreprocessors, and the lidar system 200 may be configured to, using the oneor more processors and based on the output signal, generate a digitalrepresentation of the field of view (e.g., a distance of an object fromthe lidar system and/or the like).

In some implementations, the lidar system may be a coherent lidarsystem, such as an FMCW lidar system. In some implementations, the lidarsystem (e.g., FMCW lidar system) may be associated with an autonomousmachine, such as an autonomous vehicle. As indicated above, FIG. 2 isprovided merely as an example. Other examples may differ from what isdescribed with regard to FIG. 2.

FIG. 3 is a diagram of an example lidar receiver 300 as describedherein. In particular, FIG. 3 shows a circuit associated with the lidarreceiver 300. In some implementations, a lidar system (e.g., the lidarsystem 200 of FIG. 2), a three-dimensional sensing system, and/or thelike may include the lidar receiver 300 (e.g., as the receiver shown inFIG. 2.), a transmitter (e.g., the laser, the optical system, thescanner, and/or the like as shown in FIG. 2), and one or moreprocessors. As shown in FIG. 3, the lidar receiver 300 may includephotodiode 1, photodiode 2, a first resistor R1, a second resistor R2,an optical mixer 302, a first differential amplifier (DA) 304 a, asecond DA 304 b, a first analog-to-digital converter (ADC) 306 a, asecond ADC 306 b, a processor 308, a direct-current-to-direct-current(DC-DC) converter 310, a TIA 312, a frequency filter 314, a third DA316, and a third ADC 318.

As shown in FIG. 3, the optical mixer 302 may receive an input signalassociated with a reflection of an optical beam transmitted by thetransmitter of the lidar system. In some implementations, such as inFMCW lidar, the optical mixer 302 may also receive a signal associatedwith a local oscillator of the lidar system. The optical mixer 302 mayoutput a signal associated with a difference (e.g., a heterodynemeasurement) of the input signal and the signal associated with thelocal oscillator to photodiode 1 and photodiode 2, and photodiode 1 andphotodiode 2 may generate, based on the signal associated with thedifference, a first photocurrent and a second photocurrent,respectively.

In some implementations, photodiode 1 and/or photodiode 2 may beavalanche photodiodes. For example, photodiode 1 and photodiode 2 may beavalanche photodiodes having a gain of between 1 and 1.5 (e.g., 1.1,1.3, and/or the like).

As shown in FIG. 3, the first resistor R1, the first DA 304 a, and thefirst ADC 306 a may be associated with photodiode 1. For example, thefirst DA 304 a may be connected to photodiode 1 via the first resistorR1, and may obtain a first analog signal based on the first photocurrentfrom the photodiode 1. The first DA 304 a may improve the first analogsignal prior to processing by the first ADC 306 a. The first ADC 306 amay be connected to an output of the first DA 304 a, and may derive afirst digital signal based on the first analog signal. For example, thefirst ADC 306 a may be configured to convert the first analog signal tothe first digital signal for use by the processor 308.

Similarly, and as also shown in FIG. 3, the second resistor R2, thesecond DA 304 b, and the second ADC 306 b may be associated withphotodiode 2. For example, the second DA 304 b may be connected tophotodiode 2 via the second resistor R2, and may obtain a second analogsignal based on the second photocurrent from the photodiode 2. Thesecond DA 304 b may improve the second analog signal prior to processingby the second ADC 306 b. The second ADC 306 b may be connected to anoutput of the second DA 304 b, and may derive a second digital signalbased on the second analog signal. For example, the second ADC 306 b maybe configured to convert the second analog signal to the second digitalsignal for use by the processor 308.

In some implementations, the first DA 304 a and/or the second DA 304 bmay be a low speed amplifier. For example, the first DA 304 a and/or thesecond DA 304 b may operate at a frequency of 1 kHz or less (e.g., 900Hz, 500 Hz, 300 Hz, 100 Hz, 50 Hz, 30 Hz, and/or the like).

As shown in FIG. 3, the processor 308 may be connected to an output ofthe first ADC 306 a and an output of the second ADC 306 b. In someimplementations, the processor 308 may be configured to determine, basedon the first digital signal and the second digital signal, a first biasto apply to photodiode 1 and a second bias to apply to photodiode 2. Forexample, the processor 308 may be configured to determine the first biasand the second bias such that, when the first bias is applied tophotodiode 1 and the second bias is applied to photodiode 2, the firstphotocurrent corresponds to the second photocurrent. In someimplementations, the first photocurrent may correspond to the secondphotocurrent when a ratio of the first photocurrent to the secondphotocurrent satisfies a threshold and/or when a ratio of the secondphotocurrent to the first photocurrent satisfies a threshold. Forexample, a ratio of between 0.9 and 1.1 may satisfy the threshold.

Additionally, or alternatively, the processor 308 may be configured todetermine the first bias and the second bias such that, when the firstbias is applied to photodiode 1 and the second bias is applied tophotodiode 2, a ratio of the first photocurrent to the secondphotocurrent satisfies a threshold. For example, a ratio of between 0.9and 1.1 may satisfy the threshold.

Additionally, or alternatively, the processor 308 may be configured todetermine the first bias and the second bias such that, when the firstbias is applied to photodiode 1 and the second bias is applied tophotodiode 2, a ratio of the second photocurrent to the firstphotocurrent satisfies a threshold. For example, a ratio of between 0.9and 1.1 may satisfy the threshold.

As shown in FIG. 3, the DC-DC converter 310 may be connected to anoutput of the processor and to photodiode 1 and photodiode 2. In someimplementations, the DC-DC converter 310 may be configured to receive,from the processor 308, the first bias and the second bias. In someimplementations, the DC-DC converter 310 may be configured to apply thefirst bias to photodiode 1 and apply the second bias to photodiode 2.For example, the DC-DC converter 310 may be configured to apply apositive bias corresponding to the first bias to photodiode 1 and applya negative bias corresponding to the second bias to photodiode 2. Byapplying the first bias to photodiode 1 and applying the second bias tophotodiode 2, the DC-DC converter 310 may balance the first photocurrentand the second photocurrent such that the first photocurrent correspondsto the second photocurrent.

As shown in FIG. 3, the TIA 312 may be connected to photodiode 1 andphotodiode 2. In some implementations, the TIA 312 may convert a thirdphotocurrent to an analog output signal (e.g., a voltage), where thethird photocurrent may be a combination of the first photocurrent andthe second photocurrent. In some implementations, the TIA 312 may outputthe analog output signal to the frequency filter 314.

As shown in FIG. 3, the frequency filter 314 may be connected to anoutput of the TIA 312. In some implementations, the frequency filter 314may be configured to pass a particular range of frequencies of theanalog output signal. For example, the frequency filter 314 may be aband-pass filter, a low-pass filter, and/or the like. In someimplementations, the frequency filter 314 may be configured to output afiltered analog output signal to the third DA 316.

As shown in FIG. 3, the third DA 316 may be connected to an output ofthe frequency filter 314. In some implementations, the third DA 316 mayreceive, from the frequency filter 314, the filtered analog outputsignal, and the third DA 316 may be configured to improve the filteredanalog output signal prior to processing by the third ADC 318. In someimplementations, the third DA 316 may be a high speed amplifier. Forexample, the third DA 316 may operate at a frequency of 1 MHz or more(e.g., 10 MHz, 50 MHz, 100 MHz, 200 MHz, 300 Hz, 400 Hz, 500 MHz and/orthe like). In some implementations, the third DA 316 may be configuredto output the improved filtered analog output signal to the third ADC318.

As shown in FIG. 3, the third ADC 318 may be connected to the third DA316. In some implementations, the third ADC 318 may receive the improvedfiltered analog output signal from the third DA 316, and the third ADC318 may be configured to convert the improved filtered analog outputsignal to a digital output signal.

In some implementations, the third ADC 318 may be configured to outputthe digital output signal to one or more processors (e.g., the processor308, another processor, and/or the like). The one or more processors maygenerate, based on the digital output signal, a digital representationof one or more targets (e.g., in a field-of-view (FOV) of the lidarsystem). For example, the one or more processors may process the digitaloutput signal with a fast Fourier transform (FFT) to generate thedigital representation.

In this way, the lidar receiver 300 may balance the first photocurrentand the second photocurrent to achieve an Alpha near one, a higher CMRR,an improved SNR, improved performance of a lidar system including thelidar receiver, and/or the like. For example, by balancing the firstphotocurrent and the second photocurrent, the lidar receiver 300 mayprovide a higher quality digital output signal than may be providedwithout balancing the first photocurrent and the second photocurrent.Additionally, or alternatively, by providing a higher quality digitaloutput signal, the lidar receiver 300 may conserve computing resourcesthat would otherwise be consumed by performing additional processing onthe digital output signal to generate the digital representation.

Additionally, or alternatively, the lidar receiver 300 may balance thefirst photocurrent and the second photocurrent (e.g., by adjusting thefirst bias and/or the second bias) as conditions of the lidar systemchange. For example, changes in temperature, pressure, humidity, and/orthe like may affect components of the lidar system (e.g., thetransmitter, an optical system, a scanner, and/or the like) such thatthe signal associated with the local oscillator and/or the input signalchange and affect the first photocurrent and/or the second photocurrent.In some implementations, the lidar receiver 300 may actively balance, byadjusting the first bias and/or the second bias, the first photocurrentand the second photocurrent as the conditions change. In this way, thelidar receiver 300 may maintain performance of the lidar system asconditions change.

In some implementations, manufacturing of the lidar receiver 300 may notrequire screening tests to confirm that photodiode 1 and photodiode 2provide balanced photocurrents (e.g., to confirm a higher CMRR and/orthe like) because the lidar receiver 300 may actively balance thephotodiode 1 and photodiode 2. Accordingly, the lidar receiver 300 mayconserve computing resources and/or financial resources during themanufacturing process that would otherwise be consumed by performingscreening tests on photodiode 1 and photodiode 2.

As indicated above, FIG. 3 is provided merely as an example. Otherexamples may differ from what is described with regard to FIG. 3.

FIG. 4 is a flow chart of an example process 400 for balancingphotocurrents of photodiodes in a lidar receiver. In someimplementations, one or more process blocks of FIG. 4 may be performedby a lidar receiver (e.g., lidar receiver 300). In some implementations,one or more process blocks of FIG. 4 may be performed by another deviceor a group of devices separate from or including the lidar receiver,such as a lidar system (e.g., lidar system 200), and/or the like.

As shown in FIG. 4, process 400 may include generating, based at leastin part on a reflection of an optical beam, a first analog signal (block410). For example, the lidar receiver (e.g., using photodiode 1, theresistor R1, the first DA 304 a, and/or the like) may generate, based atleast in part on a reflection of an optical beam, a first analog signal,as described above.

As further shown in FIG. 4, process 400 may include deriving, based onthe first analog signal, a first digital signal (block 420). Forexample, the lidar receiver (e.g., using the first ADC 306 a and/or thelike) may derive, based on the first analog signal, a first digitalsignal, as described above.

As further shown in FIG. 4, process 400 may include generating, based atleast in part on the reflection of the optical beam, a second analogsignal (block 430). For example, the lidar receiver (e.g., usingphotodiode 2, the resistor R2, the second DA 304 b, and/or the like) maygenerate, based at least in part on the reflection of the optical beam,a second analog signal, as described above.

As further shown in FIG. 4, process 400 may include deriving, based onthe second analog signal, a second digital signal (block 440). Forexample, the lidar receiver (e.g., using the second ADC 306 b and/or thelike) may derive, based on the second analog signal, a second digitalsignal, as described above.

As further shown in FIG. 4, process 400 may include determining, basedon the first digital signal and the second digital signal, a first biasto apply to a first photodiode and a second bias to apply to a secondphotodiode, wherein, when the first bias is applied to the firstphotodiode and the second bias is applied to the second photodiode, afirst current associated with the first analog signal corresponds to asecond current associated with the second analog signal (block 450). Forexample, the lidar receiver (e.g., using the processor 308 and/or thelike) may determine, based on the first digital signal and the seconddigital signal, a first bias to apply to the first photodiode and asecond bias to apply to the second photodiode, as described above. Insome implementations, when the first bias is applied to the firstphotodiode and the second bias is applied to the second photodiode, afirst current associated with the first analog signal corresponds to asecond current associated with the second analog signal.

Process 400 may include additional implementations, such as any singleimplementation or any combination of implementations described belowand/or in connection with one or more other processes describedelsewhere herein.

In a first implementation, the first photodiode and the secondphotodiode are avalanche photodiodes.

In a second implementation, alone or in combination with the firstimplementation, the first bias, when applied to the first photodiode,adjusts a first gain of the first photodiode, and the second bias, whenapplied to the second photodiode, adjusts a second gain of the secondphotodiode.

In a third implementation, alone or in combination with one or more ofthe first and second implementations, process 400 includes applying thefirst bias to the first photodiode and applying the second bias to thesecond photodiode. For example, the lidar receiver (e.g., using theDC-DC converter 310 and/or the like) may apply the first bias to thefirst photodiode and apply the second bias to the second photodiode, asdescribed above.

In a fourth implementation, alone or in combination with one or more ofthe first through third implementations, process 400 includes generatinga photocurrent and converting the photocurrent to an output signal. Forexample, the lidar receiver (e.g., using photodiode 1, photodiode 2,and/or the like) may generate the photocurrent, and the lidar receiver(e.g., using the TIA 312, the frequency filter 314, the third DA 316,the third ADC 318, and/or the like) may convert the photocurrent to anoutput signal, as described above.

Although FIG. 4 shows example blocks of process 400, in someimplementations, process 400 may include additional blocks, fewerblocks, different blocks, or differently arranged blocks than thosedepicted in FIG. 4. Additionally, or alternatively, two or more of theblocks of process 400 may be performed in parallel.

The foregoing disclosure provides illustration and description, but isnot intended to be exhaustive or to limit the implementations to theprecise forms disclosed. Modifications and variations may be made inlight of the above disclosure or may be acquired from practice of theimplementations.

As used herein, the term “component” is intended to be broadly construedas hardware, firmware, and/or a combination of hardware and software.

As used herein, satisfying a threshold may, depending on the context,refer to a value being greater than the threshold, more than thethreshold, higher than the threshold, greater than or equal to thethreshold, less than the threshold, fewer than the threshold, lower thanthe threshold, less than or equal to the threshold, equal to thethreshold, or the like.

It will be apparent that systems and/or methods described herein may beimplemented in different forms of hardware, firmware, or a combinationof hardware and software. The actual specialized control hardware orsoftware code used to implement these systems and/or methods is notlimiting of the implementations. Thus, the operation and behavior of thesystems and/or methods are described herein without reference tospecific software code—it being understood that software and hardwarecan be designed to implement the systems and/or methods based on thedescription herein.

Even though particular combinations of features are recited in theclaims and/or disclosed in the specification, these combinations are notintended to limit the disclosure of various implementations. In fact,many of these features may be combined in ways not specifically recitedin the claims and/or disclosed in the specification. Although eachdependent claim listed below may directly depend on only one claim, thedisclosure of various implementations includes each dependent claim incombination with every other claim in the claim set.

No element, act, or instruction used herein should be construed ascritical or essential unless explicitly described as such. Also, as usedherein, the articles “a” and “an” are intended to include one or moreitems, and may be used interchangeably with “one or more.” Further, asused herein, the article “the” is intended to include one or more itemsreferenced in connection with the article “the” and may be usedinterchangeably with “the one or more.” Furthermore, as used herein, theterm “set” is intended to include one or more items (e.g., relateditems, unrelated items, a combination of related and unrelated items,etc.), and may be used interchangeably with “one or more.” Where onlyone item is intended, the phrase “only one” or similar language is used.Also, as used herein, the terms “has,” “have,” “having,” or the like areintended to be open-ended terms. Further, the phrase “based on” isintended to mean “based, at least in part, on” unless explicitly statedotherwise. Also, as used herein, the term “or” is intended to beinclusive when used in a series and may be used interchangeably with“and/or,” unless explicitly stated otherwise (e.g., if used incombination with “either” or “only one of”).

What is claimed is:
 1. A light detection and ranging (lidar) system,comprising: a transmitter to transmit an optical beam; and a receiver toreceive a reflection of the optical beam, the receiver comprising: afirst photodiode to generate a first analog signal that is based atleast in part on the reflection of the optical beam; a first amplifierto obtain the first analog signal from the first photodiode; a firstanalog-to-digital converter (ADC) to derive a first digital signal basedon the first analog signal; a second photodiode to generate a secondanalog signal that is based at least in part on the reflection of theoptical beam; a second amplifier to obtain the second analog signal fromthe second photodiode; a second ADC to derive a second digital signalbased on the second analog signal; a processor to determine, based onthe first digital signal and the second digital signal, a first bias toapply to the first photodiode and a second bias to apply to the secondphotodiode, wherein, when the first bias is applied to the firstphotodiode and the second bias is applied to the second photodiode, afirst current associated with the first analog signal corresponds to asecond current associated with the second analog signal; and adirect-current-to-direct-current converter to apply the first bias tothe first photodiode and to apply the second bias to the secondphotodiode.
 2. The lidar system of claim 1, wherein the first photodiodeand the second photodiode are avalanche photodiodes.
 3. The lidar systemof claim 1, wherein at least one of the first amplifier or the secondamplifier is a low speed amplifier.
 4. The lidar system of claim 1,wherein the first bias, when applied to the first photodiode, adjusts afirst gain of the first photodiode, and wherein the second bias, whenapplied to the second photodiode, adjusts a second gain of the secondphotodiode.
 5. The lidar system of claim 1, further comprising: atransimpedance amplifier to convert a photocurrent to an analog outputsignal, wherein the first photodiode and the second photodiode are togenerate the photocurrent; and a third ADC to convert the analog outputsignal to a digital output signal.
 6. The lidar system of claim 1,wherein the transmitter comprises: a laser to generate the optical beam;and a scanner to scan a field of view with the optical beam and toreceive the reflection of the optical beam.
 7. A light detection andranging (lidar) receiver, comprising: a first photodiode; a firstamplifier connected to the first photodiode; a first analog-to-digitalconverter (ADC) connected to an output of the first amplifier; a secondphotodiode; a second amplifier connected to the second photodiode; asecond ADC connected to an output of the second amplifier; a processorconnected to an output of the first ADC and an output of the second ADC;and a direct-current-to-direct-current converter connected to an outputof the processor and to the first photodiode and the second photodiode.8. The lidar receiver of claim 7, wherein the first photodiode and thesecond photodiode are avalanche photodiodes.
 9. The lidar receiver ofclaim 7, wherein at least one of the first amplifier or the secondamplifier is a low speed amplifier.
 10. The lidar receiver of claim 7,wherein the first photodiode is to generate a first analog signal,wherein the first amplifier is to obtain the first analog signal fromthe first photodiode, wherein the first ADC is to derive a first digitalsignal based on the first analog signal, wherein the second photodiodeis to generate a second analog signal, wherein the second amplifier isto obtain the second analog signal from the second photodiode, andwherein the second ADC is to derive a second digital signal based on thesecond analog signal.
 11. The lidar receiver of claim 7, wherein theprocessor is to determine, based on the output of the first ADC and theoutput of the second ADC, a first bias to apply to the first photodiodeand a second bias to apply to the second photodiode, wherein, when thefirst bias is applied to the first photodiode and the second bias isapplied to the second photodiode, a first current associated with thefirst photodiode corresponds to a second current associated with thesecond photodiode.
 12. The lidar receiver of claim 11, wherein the firstbias, when applied to the first photodiode, adjusts a first gain of thefirst photodiode, and wherein the second bias, when applied to thesecond photodiode, adjusts a second gain of the second photodiode. 13.The lidar receiver of claim 7, wherein thedirect-current-to-direct-current converter is to apply, based on theoutput of the processor, a first bias to the first photodiode and toapply, based on the output of the processor, a second bias to the secondphotodiode.
 14. The lidar receiver of claim 7, further comprising: atransimpedance amplifier connected to the first photodiode and thesecond photodiode; and a third ADC connected to the transimpedanceamplifier.
 15. The lidar receiver of claim 14, wherein thetransimpedance amplifier is to convert a photocurrent to an analogoutput signal, wherein the first photodiode and the second photodiodeare to generate the photocurrent; and wherein the third ADC is toconvert the analog output signal to a digital output signal.
 16. Amethod, comprising: generating, by a lidar receiver, using a firstphotodiode, and based at least in part on a reflection of an opticalbeam, a first analog signal; deriving, by the lidar receiver and basedon the first analog signal, a first digital signal; generating, by thelidar receiver, using a second photodiode, and based at least in part onthe reflection of the optical beam, a second analog signal; deriving, bythe lidar receiver and based on the second analog signal, a seconddigital signal; and determining, by the lidar receiver and based on thefirst digital signal and the second digital signal, a first bias toapply to the first photodiode and a second bias to apply to the secondphotodiode, wherein, when the first bias is applied to the firstphotodiode and the second bias is applied to the second photodiode, afirst current associated with the first analog signal corresponds to asecond current associated with the second analog signal.
 17. The methodof claim 16, wherein the first photodiode and the second photodiode areavalanche photodiodes.
 18. The method of claim 16, wherein the firstbias, when applied to the first photodiode, adjusts a first gain of thefirst photodiode, and wherein the second bias, when applied to thesecond photodiode, adjusts a second gain of the second photodiode. 19.The method of claim 16, further comprising: applying the first bias tothe first photodiode; and applying the second bias to the secondphotodiode.
 20. The method of claim 16, further comprising: generating,using the first photodiode and the second photodiode, a photocurrent;and converting the photocurrent to an output signal.